1. Field of Invention
The invention generally relates to a mass flowmeter which operates on the Coriolis principle. The invention is specifically concerned with a compact mass flowmeter having at least three closely arranged measurement tubes which can oscillate and through which a medium can flow, at least one oscillation generator for excitation of the oscillations of the measurement tube, and at least one oscillation sensor for detection of the excited oscillations of the measurement tube.
2. Description of Related Art
Mass flowmeters which operate on the Coriolis principle have in principle been known for many years and allow the mass flow rate of the medium flowing through the measurement tube to be determined with high accuracy. In order to determine the mass flow rate, the Coriolis measurement tube is caused to oscillate by an oscillation generator or else by a plurality of oscillation generators—in particular at the natural frequency of one specific eigen form of an oscillation—and the oscillations which actually result are detected by means of oscillation sensors, and are evaluated. By way of example, the evaluation process comprises determination of the phase shift between the oscillations detected by each of the two oscillation sensors, with this phase shift being a direct measure of the mass flow rate. Coriolis mass flowmeters are known which have a single measurement tube, as well as those which have two and only two measurement tubes, with the measurement tubes either extending essentially in a straight line or being curved. Mass flowmeters with two measurement tubes have the advantage that—assuming that the measurement tubes, which are arranged adjacent, are excited in antiphase—the center of gravity of the system which is caused to oscillate remains unchanged overall, and the mass flowmeter is therefore externally mechanically neutral.
Depending on the quantity of the masses to be transported, the measurement tubes of the mass flowmeters have wildly differing nominal widths with different wall thicknesses. The measurement tubes must be designed overall such that they can withstand the necessary pressures and mechanical stresses that occur, and can be excited to oscillate in a manner which can be detected well with an acceptable consumption of energy. The measurement tubes must be further be designed such that that the natural frequencies of the measurement tube through which the flow passes are in a desired range, and the measurement tubes do not cause unacceptable resistance to the mass flow. In order to allow relatively high mass flows to be detected, it is not simply possible just to increase the nominal widths of the measurement tubes of a known mass flowmeter, since this automatically changes the oscillation behavior of the measurement tubes. In consequence, an increase in the nominal width of measurement tubes is frequently associated with the measurement tube being lengthened, resulting an increase in all of the dimensions of the mass flowmeter.